Because of its durability, flexibility, and economy, masonry is still the most popular system for prison and jail construction. Most correctional facilities feature cavity walls with fully grouted and reinforced concrete masonry backup wythes and block or clay brick veneers. Interior walls typically consist of concrete masonry units, which are grouted and reinforced in high-security areas: Concrete block is used in inmate cells, dayrooms, control rooms, laundries, warehouses, multipurpose rooms, visitors' facilities, and other enclosures. Masonry's durability is extremely important in correctional design, as prisons and jails are intended to last more than 100 years. But flexibility is the critical benefit that sets masonry apart from the competing building systems. Masonry also allows enclosures of different shapes and dimensions to be constructed easily. The major trend in prison design today favors masonry. The linear facilities of the past have given way to modular configurations of self-contained pods, where inmates are under the "direct supervision" of correctional officers. This minimizes inmate movement and the number of guards required for supervision, while improving security. Masonry lends itself to such complicated, odd-shaped structures.